The present invention refers to a device and a method for measuring the extension or contraction properties of filamentous specimens.
Such testing apparatus are known, for example, under the name xe2x80x9cDynafilxe2x80x9d and are available from Textechno, Mxc3x6nchengladbach Germany (Textile Asia, March 1981, Business Press Limited: Continuous Tester). In these testing apparatus, the filamentous specimens are supplied through a heating tube under adjustable extension or overfeed (shortening) that is constant throughout the test or without an alteration in length, the occurring tensile force being continually measured. Depending on the test parameters set and on the type of specimen, various test methods may be obtained:
draw force test of pre-oriented or fully stretched yarns,
crimp force test of textured yarns, and
shrinkage force test of flat and textured yarns.
Another known testing apparatus by the name TYT, available from Lawson Hemphill, continually measures the alterations in length of a filament yarn under constant tensile force while the yam passes through a closed heating tube. Preferably, this test is used to determine the crimp contraction of textured yarns.
The known apparatus comprise a test section formed by an inlet and an outlet delivery device and the intermediately arranged heating tube, as well as the force sensor (DYNAFIL) or the device for keeping the filament tensile force constant (TYT). The supply rates of both delivery devices may be varied in common or relative to each other.
The melting temperature of the fiber materials usually subjected to such tests is 260xc2x0 C. at maximum (polyester, nylon 6.6). Therefore, the heating tube temperature of the known test apparatus must always be set below this limit value. Otherwise the yarn would melt and tear in the heating tube when the apparatus is at a standstill or running slowly, as well as when a new specimen is introduced into the test section.
Due to this limitation of the heating tube temperature, the maximum possible filament speeds, at which the yarn is still heated to the degree necessary for the test, are limited, too. Depending on the count of the yarn, 100 to 200 m/min can be reached.
Starting from this prior art, it is an object of the present invention to improve testers of the type mentioned above such that, on the one hand, substantially higher test speeds are possible and, on the other hand, high temperature resistant specimens can be tested.
Advantageously, the invention provides that a positioning means displaces the filamentous specimen relative to the heating means or the heating means relative to the filamentous specimen such that, in an end position, the specimen is placed within the heating means and, in the other end position, the specimen is placed outside the heating means.
To this effect, the heating means is not designed as a closed tube as with conventional testers. Rather, it comprises a heating channel with a lateral slot for inserting and removing the specimen, the slot being adapted to be opened and closed automatically.
Such a positioning means in connection with the heating means allows for heating temperatures far above the melting temperatures of the fiber materials, e.g. up to 800xc2x0 C., and thus much higher filament speeds, e.g. up to 1000 m/min, at which the filament reaches the optimum temperature. When the running of the filamentous specimen is to be stopped or a new specimen is to be placed into the test section, the positioning means first moves the specimenxe2x80x94still running at a high speedxe2x80x94out of the heating means. Upon restarting the device, the specimen is first accelerated to the test speed outside the heating means and introduced into the heating channel thereafter. In this manner, melting and tearing of the fibre material in the heating means are excluded.
Another advantage of such a high-temperature heating means is that it also allows for the testing of high-temperature resistant fiber materials. Testing such materials in the known apparatus at relatively low heating temperatures does not yield any useful test results.
The delivery devices of the present tester may be motor-driven godets or feed rollers with aprons or nip rolls.
In a development of the invention, it is provided that additional measuring means are arranged in the test section between the inlet and the outlet delivery device, in front of the inlet delivery device, seen in the running direction of the specimen, or behind the outlet delivery device. These additional measuring means serve to measure friction, filament breaks, entanglements, yarn evenness or yarn count.
In a preferred embodiment, it is provided that a means for adjusting and maintaining constant a predetermined pre-tensioning force in the running specimen is arranged in front of the first delivery device, seen in the running direction of the specimen, which may be controlled by the measuring signal from the force sensor picked from the test section. This means ensures an exactly adjustable pre-tensioning force constant during the test.
Behind the heating means, seen in the running direction of the specimen, a temperature sensor may be disposed for determining the actually reached specimen temperature. This temperature sensor provides a measuring signal suitable for the temperature control of the heating means.
Further, behind the heating means, seen in the running direction of the specimen, a twisting means for generating a false twist in the specimen may be provided.
The device of the present invention joins the different test methods of the known test apparatus in one apparatus. In measuring the running filamentous specimen, tests with constant extension or contraction of the specimen and a simultaneous measuring of the force occurring in the specimen become possible. Alternatively, the test may be effected using a constant tensile force acting on the specimen, the speed of at least one of the two delivery devices being continually adjusted. The variation in length of the specimen, which at all times corresponds to the difference in speed between the two delivery devices, is measured continually.
At heating temperatures below the melting temperature of the specimen, testing of the standing specimen is also possible. Herexe2x80x94after insertion of the specimen into the testerxe2x80x94either without change in length or with a constant change in filament length, force is measured in relation to time, or, with the force maintained constant, the change in length is measured in relation to the time.
In measurements of the standing specimen, an essential advantage of the present invention is that a subsequent measurement may be effected very fast by introducing a new specimen section by means of the delivery devices.